import { useEffect, useMemo, useState } from "react";
import { activeLyricIndex, parseLrc } from "../lrc-parser/lrc-parser.js";
import type { Lyric } from "../lrc-parser/lrc-parser.types.js";
import type { UseLyricsOptions, UseLyricsResult } from "./use-lyrics.types.js";

const DEFAULT_INTERVAL_MS = 100;

/**
 * Engine-agnostic karaoke hook. Accepts a pre-parsed `lyrics` array
 * (preferred) or a raw `lrc` string, plus a `currentSec` value, and
 * returns the active line. Sampling cadence is decoupled from the
 * caller's render rate: a 100 ms interval (configurable) forces a
 * re-render even when neither `lyrics` nor `currentSec` mutate.
 *
 * The hook is deliberately decoupled from `useTransportTime` so it
 * can be driven from any clock — `<LyricsDisplay>` wires the
 * transport in for you when used inside `<AudioProvider>`, but a
 * preview panel running under a deterministic test clock can call
 * this hook directly with a hand-fed `currentSec`.
 */
export function useLyrics(opts: UseLyricsOptions): UseLyricsResult {
    const lyrics: readonly Lyric[] = useMemo(() => {
        if (opts.lyrics) return opts.lyrics;
        if (typeof opts.lrc === "string") return parseLrc(opts.lrc);
        return [];
    }, [opts.lyrics, opts.lrc]);

    const intervalMs = opts.intervalMs ?? DEFAULT_INTERVAL_MS;

    // A heartbeat counter forces a re-render every `intervalMs` so
    // the memo below recomputes even when `currentSec` did not
    // change between commits — relevant when the consumer's clock
    // mutates a ref or external store the hook cannot subscribe to.
    const [, setTick] = useState(0);

    useEffect(() => {
        const id = setInterval(
            () => {
                setTick((t) => (t + 1) % 1_000_000);
            },
            Math.max(1, intervalMs)
        );
        return () => {
            clearInterval(id);
        };
    }, [intervalMs]);

    const activeIndex = useMemo(
        () => activeLyricIndex(lyrics, opts.currentSec),
        [lyrics, opts.currentSec]
    );

    return {
        lyrics,
        activeIndex,
        activeLyric: activeIndex >= 0 ? lyrics[activeIndex] : undefined,
    };
}